Laboratory host specificity testing of the fire ant microsporidian pathogen Vairimorpha invictae (Microsporidia: Burenellidae)

The host specificity of Vairimorpha invictae, a microsporidian pathogen of fire ants in South America, was assessed in the laboratory. Species evaluated included the tropical fire ant, Solenopsis geminata, the southern fire ant, Solenopsis xyloni, and the Argentine ant, Linepithema humile. The two fire ant species are native to North America. The Argentine ant is a widespread, exotic species that co-occurs with the native North American fire ants as well as with the red imported fire ant, Solenopsis invicta, and the black imported fire ant, Solenopsis richteri, in the US. Inoculations of V. invictae-infected S. invicta brood to laboratory colonies did not result in any infections of S. geminata, S. xyloni, or L. humile, while 60% of the S. invicta colonies developed infections. V. invictae was not detected in smaller groups of S. geminata and S. xyloni larvae that were tended by V. invictae-infected adult, S. invicta workers, but was detected in 40% of the S. invicta larval groups tended by infected workers. This was the first report of V. invictae transmission to larvae by infected adult worker ants. Exposure to V. invictae by contact with infected brood and workers partially emulated possible field interactions between infected and uninfected ant species. These results are congruent with previous field surveys which indicate that the host range of V. invictae is limited to fire ants of the Solenopsis saevissima species group.